1. Field of the Invention
The present invention relates to a curable composition comprising the use of a cyclic diamine in fast-curing epoxy formulations.
2. Description of Background and Related Art
N-aminoethylpiperazine (AEP) is a compound that is known to be used as an “accelerator” for assisting the cure of epoxy/amine-based formulations. Much has been made of the unique attributes of AEP such as the fact that AEP contains primary, secondary and tertiary amine groups that allow AEP to help rapidly cure epoxy/amine-based formulations. Other substituted piperazine molecules have been evaluated as a substitute for AEP for epoxy/amine-based formulations, but none of the known piperazine molecules have offered the same accelerating effects as AEP.
In column 1, lines 35-37 of U.S. Pat. No. 6,946,503 (the '503 patent), it states: “Shortages of AEP have created a need for a substitute material that can serve to accelerate the curing reaction of slower amine curatives (e.g., JEFFAMINE® brand amines).” Column 1, lines 61-63 of the '503 patent further states: “[AEP] has provided some of the highest exotherm temperatures seen when used to cure epoxy resins.” The '503 patent, and others references listed herein, have tried to duplicate this degree of reactivity by replacing AEP with various alternative compositions, particularly when the principal curing agent is a JEFFAMINE-type (polyoxyalkylene polyamine) curing agent. However, end use applications dictate the type of curing agent and the degree of acceleration that is needed for a curable epoxy resin formulation to exhibit the desired properties in the time frame required by the end use application. Although known polyoxyalkylene polyamines are frequently used in many applications, the polyoxyalkylene polyamines are by no means the only amine curing agents that need to be accelerated. There are various known methods to accomplish these ends. However, for known AEP-based epoxy formulations, no single substitute has been found that is universally acceptable in all the applications where AEP is used because of its reactivity. Therefore, work continues to find suitable replacements for AEP in different applications.
It would be desirable to provide a substitute for AEP for certain end use applications such as civil engineering applications. Civil engineering applications, such as road traffic markers applications which use an epoxy/amine resin formulation, are applications that require fast cure of the resin formulation so that traffic can resume driving over the roads in a relatively short period of time. One example of such a formulation is disclosed in AASHTO Designation M 237-96 entitled “Epoxy Resin Adhesives for Bonding Traffic Markers to Hardened Portland Cement and Asphalt Concrete.” The resin adhesive is designated as “Type IV Epoxy” and uses AEP as the sole amine curing agent. Other related applications which might use this type of resin formulation include pavement markings and bridge deck overlays.
U.S. Pat. No. 3,875,072 (the '072 patent) discloses a piperazine and alkanolamine accelerator for epoxy curing. The '072 patent deals with curing epoxy resins with a JEFFAMINE-type curing agent using a synergistic accelerator mixture consisting of piperazine and an alkanolamine. The '072 patent states that it is essential that the weight ratio of piperazine to alkanolamine be in the range of 1:8 to 1:1. The '072 patent also teaches that preferably the combined amount of N—H from the JEFFAMINE, piperazine and alkanolamine will provide up to a 10% excess of the stoichiometric amount needed to cure the epoxy. The '072 patent also teaches that the mixture containing the epoxy, polyoxyalkylene polyamine, piperazine and alkanolamine can be allowed to self-cure at ambient room temperatures of between about 0° C. to about 45° C. The '072 patent also discloses that the mixture can be cured or post-cured at elevated temperatures of up to about 175° C., if desirable or convenient. The '072 patent covers a composition. The end-use applications cited in the '072 patent are protective coatings, adhesives, seamless and terrazzo flooring, castings, laminates, and in grouting, potting, encapsulating, caulking and sealing compositions. The '072 patent does not disclose that non-heterocyclic amines with pKa values greater than 9.5 to about 12 can lead to significantly enhanced reactivity when combined with the cyclic diamines.
U.S. Pat. No. 3,943,104 (the '104 patent) discloses a method of accelerating epoxy curing. The teachings in '104 patent are essentially the same as in U.S. Pat. No. 3,875,072 described above, except that the '104 patent covers a process of using an accelerator mixture.
U.S. Pat. No. 4,189,564 (the '564 patent) discloses a non-crystallizing epoxy resin accelerator. The '564 patent states, in column 1, lines 53-57, that “U.S. Pat. Nos. 3,875,072 and 3,943,104 disclose an accelerator comprising piperazine and an alkanolamine. This accelerator combination has one disadvantage. It tends to crystallize at low temperature, thus reducing its usefulness in some cases.” In column 4, lines 15-20, of the '564 patent further states that “An improvement in crystallizing tendency over the above will take place once any amount of N-aminoethylpiperazine is present with a piperazine, alkanolamine mixture. Therefore, my invention includes mixtures of piperazine, N-aminoethylpiperazine (AEP) and an alkanolamine where AEP is present.” The '564 patent teaches both a composition and a process. The use of AEP to help suppress crystallization precludes this from being an AEP-free composition of matter.
U.S. Pat. No. 4,800,222 (the '222 patent) discloses an accelerator for use with curing agents and resins including piperazine, triethanolamine and tris(dimethylaminomethyl)phenol. The '222 patent covers a composition “comprising an epoxy resin and an accelerator comprising 50-60 parts by weight treithanolamine, 20-30 parts by weight tris(dimethylaminomethyl)phenol and the balance piperazine.” In all of the '222 patent's working examples a large amount of a JEFFAMINE product is used as the curing agent. The '222 patent does not disclose that non-heterocyclic amines with pKa values greater than 9.5 to about 12 can lead to significantly enhanced reactivity when combined with the cyclic diamines.
U.S. Pat. No. 4,828,879 (the '879 patent) discloses a polymer concrete composition for cementitious road repair and overlay. The abstract of the '879 patent states: “A polymer concrete system has been discovered which is useful in road overlay and repair. The binder for this aggregate-filled system consists of a liquid epoxy resin and triethyleneglycol diamine or tetraethylene glycol diamine curing agent. A piperazine accelerator ensures adequate strength development after short cure times at ambient temperatures. The binder-aggregate system is relatively flexible, has excellent compression and flexural strength and adheres well to the substrate. The system of the '879 patent is distinguished by its fast cure to a compression strength of 3000 psi which will support automotive traffic.” In column 2, lines 54-65 of the '879 patent, it states: “The binder formulation of this invention is a low viscosity system which cures rapidly. High filler loadings are possible and compression and flexural strength develop quickly even at lower temperatures, e.g. 40° F. The coefficient of thermal expansion of a polymer concrete containing this binder system closely resembles that of Portland cement concrete up to about 120° F. Polymer concrete overlays containing this binder system resist delamination from a Portland cement concrete substrate during freeze-thaw cycling. Nonylphenol may be used in this application because it improves flexibility.” The accelerator used in the examples of the '879 patent is known as “Accelerator 399” and is a mixture of 10-20% piperazine and 5-10% N-aminoethylpiperazine in triethanolamine. This accelerator is also described in U.S. Pat. No. 4,189,564. The '879 patent covers both a method and a binder composition. The '879 patent does not disclose that non-heterocyclic amines with pKa values greater than 9.5 to about 12 can lead to significantly enhanced reactivity when combined with the cyclic diamines.
U.S. Pat. No. 4,835,241 (the '241 patent) discloses an epoxy coating using an acrylate ester, a polyetherpolyamine and a piperazine(s). According to the abstract of the '241 patent an epoxy resin composition is used as a coating composition. The composition consists of a mixture of a bisphenol A-based epoxy resin and an acrylate ester that is reacted with a mixture of a Jeffamine-type polyoxyalkylene polyamine and piperazine. In column 2, lines 41-42, the '241 patent states: “The curative additionally comprises a piperazine accelerator in molar equivalence with the acrylate ester.” In column 9, lines 38-39 of the '241 patent, it states: “The reactive amines with the best overall properties were piperazine and AEP.” In column 5, lines 49-52 and column 6, lines 1-8, the '241 patent states: “The piperazine compound is incorporated in an amount which will ensure a maximum level of primary amine reaction but give a reaction product which is not too viscous to handle. The greater the ratio of accelerator to acrylate ester, the less primary amine is reacted. However, a large excess of epoxy resin will result in a very viscous product or even a gel which is undesirable. However, excess piperazine compound is undesirable because of extraneous reactions. Accordingly, the instant coatings are formulated with piperazine compound in an approximate equivalence with the acrylate ester.” The acrylate ester used in the examples of the '241 patent is TMPTA (trimethylolpropane triacrylate). The '241 patent does not disclose the use of alkylated phenolic compounds in combination with certain proportions of the selected cyclic diamines disclosed in this document for enhancing reactivity. The '241 patent also does not disclose that non-heterocyclic amines with pKa values greater than 9.5 to about 12 can lead to significantly enhanced reactivity when combined with the cyclic diamines.
U.S. Pat. No. 4,904,711 (the '711 patent) discloses a polymer concrete composition for cementitious road repair and overlay. The teachings in the '711 patent are essentially the same as in U.S. Pat. No. 4,828,879, except that the '711 patent discloses a composition that combines both a binder and an aggregate.
U.S. Pat. No. 6,946,503 (the '503 patent) discloses an amine blend accelerator for a polyoxyalkylenepolyamine-cured epoxy resin. The abstract of the '503 patent states: “Provided herein are amine blends which may be used in place of N-aminoethylpiperazine as accelerator in the curing reaction of epoxy resins.” The key blend of the '503 patent is a mixture of 4-(3-aminopropyl)morpholine (APM) and 2-2(aminoethylamino)ethanol (AEEA). The '503 patent discloses a process for producing a cured epoxy polymer with a Jeffamine-type curing agent and an accelerator mixture consisting of APM and AEEA. The '503 patent does not provide any data indicating that the blend composition acts similarly to AEP either in terms of reactivity or properties. In addition, the '503 patent does not disclose the use of alkylated phenolic compounds in combination with certain proportions of the selected cyclic diamines disclosed in this document for enhancing reactivity.
WO 2008/103868 discloses an accelerator for the polymerization of an epoxy resin. The detailed description in WO 2008/103868 states: “[0014] Embodiments of the present invention disclose an accelerator composition have at least one amine and a glycerin. The at least one amine may comprise AEP. However, a wide variety of other amines can be used in the accelerator compositions of this invention. Combinations of two or more amines can be used.” WO 2008/103868 also teaches the use of glycerin. WO 2008/103868 does not disclose the use of alkylated phenolic compounds in combination with certain proportions of the selected cyclic diamines disclosed below for enhancing reactivity.
Accordingly, there is still a need in the industry to develop a suitable replacement for AEP that has use in compositions containing non-heterocyclic amines with pKa values greater than 9.5 to about 12.